This part deals with the core electronics of VARUN. It involves extensive usage of technologies like serial communication using UART modules, DC motor control using output compare module (CCP). Data interpreting and serial interfacing protocols have also been used. The 1^st generation vehicle employed dsPIC (PIC 30f-6014A) manufactured by microchip for depth control, locomotion and sound processing. It had a 16-bit onboard ADC(analog to digital conversion) module, along with 16-bit UART module which was used for RS-232 serial communication. It also had separate PWM modules. dsPIC was used as the central conrol unit of VARUN. However, due to troublesome debugging and operation, it has been replaced by a single board computer. The single board computer (Kontron 986 LCD-N) is the core unit of the 2^nd generation vehicle. An 8-bit PIC microcontroller (PIC16F877A) from the same manufacturer has been used for speed control of the motors. It has a separate PWM module and can be used to control the speed and direction of motor by considering the PID values sent over RS-232 from the control algorithm running in the SBC.

 Thruster and motor control

Brushed thrusters and simple dc motors have been used for providing locomotion. Control parameters for control of thrusters by PID method of motor control are acquired and thrusters output is thus controlled using H-bridges(using switching action of transistor). Simple DC motor has been employed in marker dropper mechanism. The thrusters, while in operation generate back emf. Safety circuits have been put in action to prevent any damage to the electronics circuit.

Underwater Acoustics

The SONAR system flow diagram contains essentially a receiver, which may have a pre-amplifier, followed by analogue to digital conversion. This is followed by data acquisition, processing and decision making process. The data Acquisition card used is NI PCI 4462, which features 24-bit resolution ADCs with 118dB dynamic range, 6 gain settings, variable anti-aliasing filters and 4 simultaneously samples analogue inputs at up to 204.8kS/s. Multilateration technique for pinger detection has been employed for accurately homing on to the acoustic source.

Inertia Measurement Unit (IMU)

This sensor gives both orientation and calibrated data. Orientation data implies to data related to three degrees of freedom of AUV, while calibrated data includes values of acceleration, gyro magnetic value and earth’s magnetic field in X,Y and Z axes. Motion tracker Inertial Unit manufactured by Xsens (Xsens MTi)has been used for the purpose. It communicates with the computer via serial cable

Pressure Sensor

A fully digital temperature and linearity compensation accurate pressure sensor from Desert Star (Desert Star SSP1) has been used to gauge the pressure, hence the height of the AUV below water level. It sends output to the computer via RS-232 port, and has user configurable sample rate and pressure units.

Acoustic Sensor

The acoustic sensor used in VARUN are four hydrophones from Reson (Reson TC4013). They have high sensitivity and provide uniform omni-directional sensitivities in both horizontal and vertical planes upto high frequency, and can be individually calibrated.